The invention relates to a method for producing multilayer contact electrodes for compound semiconductors. The invention also relates to such a multilayer contact electrode and to compound semiconductors equipped with such a multilayer contact electrode.
Japanese Patent Abstracts Publication JP 11-054843 a, JPO, 1999 discloses a method for producing multilayer contact electrodes for the p-type semiconductor layer of a semiconductor body made of a III/V-compound semiconductor. In the known method first a metallized layer is applied on the p-type semiconductor layer. The metallized layer is then exposed to a heat treatment or tempering at a temperature of 400xc2x0 C. Thereafter, further layers consisting of different metals including a barrier layer 13 of titanium are applied to the first metallized layer.
Japanese Patent Abstract Publications JP 62-35587 A, E-522, 1987, Vol. 11, No. 212 describes a multilayer contact electrode for a light emitting semiconductor element. A first tempered metallized layer of chromium is first applied to the semiconductor element, whereupon two further layers of germanium and gold are applied to the first layer. In a further step the further layers are etched.
German Patent Publication DE 198 20 777 A1 describes a wire bonding electrode for the surface of a p-type compound semiconductor on the basis of GaN (gallium nitride) which may have a multilayer structure, the uppermost layer of which is made of aluminum or gold.
In the European Patent Publication EP 0,952,617 A1 several different contact electrodes are disclosed for p-type layers of a III/V-compound semiconductor on the basis of InAlGaN.
Japanese Patent Abstract Publication JP 063 00 84 125 A, JPO and Japio 1988, describes a method for producing an electrode with an aluminum layer for a compound semiconductor.
Present FIG. 5 shows a conventional multilayer contact electrode on a semiconductor body 11 according to the prior art. A single layer contact electrode 13 is applied to the backside of the n-type substrate 12 to form a backside contact. A front side contact is formed as a multilayer contact electrode including a metallized layer 16A, a diffusion barrier layer 16B and a bonding pad 16C to be described in more detail below. The metallized layer 16A is either made of a gold alloy or of pure aluminum.
European Patent Publications EP 0,386,775 A1 or EP 0,584,599 A1 discloses the use of gold alloys for contact electrodes. The use of gold alloys for this purpose has the disadvantage that during the tempering of the contact electrode 16 contaminations can diffuse into the gold alloy. This diffusion applies particularly where the semiconductor layer 14 contains gallium which diffuses out of the semiconductor layer 40 into the contact metal surface where the diffused gallium oxidizes. Such oxidization causes substantial problems during wire bonding because the wire bonds do not stick to the oxide layers, whereby many wire connections are faulty and become rejects. In order to prevent the diffusion and oxidation primarily of gallium, it is necessary to provide the surface contact layer with a diffusion barrier, 16B as will be described in more detail below with reference to FIG. 5.
Further disadvantages of gold alloys for the above purpose reside in the fact that the multilayer contact electrode 16 can be structured only in several process steps, thereby using different etching solutions. Such etching procedures, due to their nature, lead to undesirable and hard to control under etching, which means etching of lower layers in the multilayer contact electrode.
The contact electrode 16 made of pure aluminum, although simpler and less expensive in its manufacture, must however be subjected to a thermal treatment at relatively high temperatures in order to form an ohmic contact with the compound semiconductor. The thermal treatment of the aluminum makes the aluminum brittle and on the surface of the contact a film is formed which contains gallium oxide and aluminum oxide as well as hydroxide, whereby the attachment of a bonding wire is again impaired and difficult.
As is known from German Patent Publication DE 32 00 788 C2 or the above mentioned European Patent Publication EP 0,584,599 A 1 , it is possible to combine a gold alloy and pure aluminum for the formation of the multilayer contact electrode 16. However, the formation of intermetallic phases lead to a problem of reliability during operation of semiconductor components provided with such gold alloy and pure aluminum combinations. Thus, it is customary to separate the gold or gold alloy from the aluminum by a diffusion barrier 16B made of titanium nitride or a titanium tungsten alloy. The manufacture and subsequent structuring or shaping of a multi-layer contact electrode 16 made of several metals is relatively expensive, particularly due to the need for a diffusion barrier 16B. The production of such a layer is involved and time consuming so that cost increases are unavoidable.
In view of the above it is the aim of the invention to achieve the following objects singly or in combination:
to provide a method for the production of multilayer contact electrodes applied to a p-type semiconductor layer of a semiconductor body made of a III/V-compound semiconductor in such a way that a simply structured contact electrode is assured and that diffusion problems are avoided without the need for a barrier layer;
to construct the contact electrode in such a way that the contacting or bonding with a bonding wire is assured without any problems and so that a reliable bond results;
to provide a contact electrode, especially structured for a p-type semiconductor layer of a III/V-compound semi-conductor; and
to provide a multilayer contact electrode that is, subsequently to its manufacture, easily structured or shaped for the intended purpose of wire bonding.
The multilayer contact electrode is produced according to the invention by first metallizing the p-type surface layer of the III/V-compound semiconductor body and then tempering the first metallized layer, whereupon a second metallized layer is applied which is not tempered and whereby both metallized layers are made of the same material such as pure aluminum, for example.
The finish electrode according to the invention comprises a first tempered metal layer or tempered metallized layer covered by a second untempered metallized or metal layer, and both layers are made of the same metal material.
A semiconductor component according to the invention combines the above defined contact electrode with a semiconductor body having a p-type semiconductor layer and itself is made of a III/V-compound semiconductor selected from the group of gallium arsenide or gallium aluminum arsenide.
The present method of manufacturing the multilayer contact electrode is simple in its nature and therefore the electrode is easily produced in economical ways because the multilayer or the two layers are made of the same metal of which only the first or inner layer is tempered. Furthermore, the need for a diffusion barrier layer has been avoided, which also is an economical advantage.
Another advantage of the invention is seen in that the present contact electrode assures a reliable bonding with a bonding wire. Moreover, the present semiconductor components equipped with the present contact electrode are particularly suitable for the manufacture of diodes for emitting infrared radiation. Such diodes are especially used of the wireless transmission of data or in various types of sensors.